As is well known, in imaging apparatuses which can obtain moving images such as digital cameras, it is performed to execute noise reduction processing for an image signal of a frame obtained by imaging a subject, and thereby reduce a noise component of the image signal and improve the signal-to-noise ratio (SNR) thereof.
In recent years, a cyclic noise reduction technique has been widespread as one of such noise reduction processing. This is a technique in which a difference between an input image signal forming a frame and an image signal forming the previous frame is multiplied by a cyclic coefficient (KNR), a multiplication result is added to the input image signal, and thereby the SNR is improved.
In the meantime, in the cyclic noise reduction technique, it is known that persistence of vision increases as the cyclic coefficient increases, while the noise reduction effect is increased as the cyclic coefficient increases. Therefore, in the present circumstances, a movement component and a noise component are determined from a difference between image signals forming the former and the latter successive frames, persistence of vision is suppressed by reducing the value of the cyclic coefficient in a part including the movement component, and noise reduction effect is increased by increasing the value of the cyclic coefficient in a part including the noise component.
In the meantime, the processing technique of determining a movement component and a noise component from a difference between image signals forming the former and the latter successive frames as described above is still at a stage of being developed, and must be regarded as having low reliability in determination result. The above technique has much room for improvement in various points to further improve the determination accuracy and for practical use.